Method for displaying a figure in a cathode ray tube on a numerical control system

ABSTRACT

A method of displaying a figure on the screen of a CRT of an NC system so that an operator can easily confirm whether or not a machining locus which is formed by a machining path of a wire electrode in a wire cut electric discharge machining apparatus during an operation of machining a workpiece to be machined according to an NC program, includes a closed loop machining path. The closed loop may cause undesired deformation of the workpiece finally machined. With such an NC controlled machining system, an accurate correction for the machining locus can be accomplished with ease, and therefore the machining apparatus is high in reliability and operability.

This is a divisional of application Ser. No. 07/417,944 filed Oct. 6,1989, now U.S. Pat. No. 5,218,548.

BACKGROUND OF THE INVENTION

This invention relates to a method for displaying a figure on the screenof a cathode ray tube (CRT) for use in a numerical control (NC) system.More particularly, the invention relates to a method of displaying afigure on the screen of the CRT of the NC system so that an operator caneasily confirm whether or not the figure (a machining locus), which isformed by a machining path of a machining tool (that is, a wireelectrode in a wire cut electric discharge machining apparatus) duringan operation of machining a workpiece to be machined according to an NCprogram, includes a closed loop machining path.

FIG. 1 is a block diagram for showing the construction of an NC systemused for a conventional wire cut electric discharge machining apparatus(hereunder abbreviated as WEDM) apparatus. In this figure, referencenumeral 1 designates a central processing unit (CPU) for processingvarious data received from other input units; 2, a memory for storingvarious data; 3, a paper tape input-output (I/O) unit for punching papertape and reading information recorded in punched paper tape; 4, a CRTfor displaying various information; 5, a keyboard for inputting data,instructions, commands and so on; 6, an I/O unit; 7, a flexible disk forreceiving and storing data through the I/O unit 6 and outputtingtherethrough; 8, a data bus for transmitting the data; and 9 a WEDMapparatus for machining a workpiece according to the NC program.

Next, an operation of this conventional NC system will be describedhereinbelow.

First, an NC program and data input from the paper tape I/O unit 3, thekeyboard 5 and the flexible disk 7 through the I/O unit 6, are analyzedin the CPU 1 so that data representing a machining locus of a wireelectrode of the WEDM apparatus on the surface of the workpiece areobtained. Thereafter, the data representing the machining locus aresubjected to a wire radius modification processing to obtain actual NCdata for driving and controlling the wire electrode of the WEDMapparatus. In the wire radius modification processing, the actual NCdata which represents an actual locus of the center of a wire electrodeduring the machining operation, is obtained by adding both the radius ofthe wire electrode and a discharge gap to the NC data representing themachined configuration of the workpiece. The actual NC data are thentransmitted to the WEDM apparatus 9 through the data bus 8. Further, theCPU 1 can control the CRT 4 to display a graphic form of the machininglocus as shown in FIG. 2 on the basis of the NC data transmitted to theWEDM apparatus 9. FIG. 3 is a schematic diagram showing an enlarged viewof details of a portion P_(A) in FIG. 2. In FIG. 3, a wire path 100(A-B-C-D) indicates the configuration finally machined according to theNC programs. Further, as described above, it is usual in the wire cutelectric discharge machining operation to modify the wire path accordingto the wire radius modification processing to obtain the actual NC datarepresenting the machining locus of the wire electrode by way ofshifting the wire path by a sum of the wire radius and the dischargegap. The machining locus modified in this way is shown by a dashed line101 and 102 (A'-B'-C'-D') in FIG. 3. As is apparent from this figure, inthe case where the original wire path (A-B-C-D) is modified with a wireradius modification h larger than a radius r of an arc portion B-C,there occurs a closed loop 102 (E'-B'-C') in the modified machininglocus 101 (A'-B'-C'-D'). This closed loop 102 causes an excessivecutting or uncutting to occur in the machined workpiece, as a result ofwhich the configuration of the thus machined workpiece is different fromthe desired configuration of the workpiece machined according to the NCprogrammed data, that is the instructed machining configuration. Thisresults in occurrence of defects or other trouble in the EDM operation.It should be noted that it is difficult to detect the occurrence of sucha closed loop in the modified machining locus from the graphic displayshown in FIG. 2.

In the conventional NC system, the wire path is displayed on the screenof the CRT in such a manner as described above. Hence, the conventionalmethod for displaying the wire path by using the CRT of the NC system isdisadvantageous in that it is difficult to readily detect whether or notthere occurs a closed loop in the machining locus which may cause adeformation in the workpiece machined according to the actual NC dataafter the wire radius modification processing.

SUMMARY OF THE INVENTION

The present invention is accomplished to eliminate the above describeddrawback accompanying the conventional method for displaying the wirepath on a CRT of the NC system.

It is accordingly an object of the present invention to provide a methodfor displaying a machining locus of a wire electrode for shaping aworkpiece into a configuration defined by an actual NC program on thescreen of a CRT of an NC system, in which it is easily possible for anoperator to confirm whether or not there occurs a closed loop in themachining locus of the wire electrode after a wire radius modificationprocessing, which may ultimately cause the deformation of the workpiecemachined.

The above, and other objects of the present invention, are accomplishedby the provision of a method for displaying a wire path for shaping aworkpiece into a form defined by a NC program on the screen of a CRT ofan NC system in which it is determined whether or not a closed loop ispresent in a wire path and, if present, segments composing the closedloop are displayed on the screen of the CRT in a color different fromthe color used for showing segments of the wire path other than theclosed loop.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparent from the following description of a preferred embodimentwith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout the several views.

In the accompanying drawings:

FIG. 1 is a schematic block diagram for showing the construction of aconventional NC system for use in a wire cut electric dischargemachining apparatus;

FIG. 2 is a diagram for showing an example of a wire path (machininglocus) for machining a workpiece into a shape defined by an NC program;

FIG. 3 is a schematic diagram showing an enlarged view of details of aportion P_(A) shown in FIG. 2;

FIG. 4 is a schematic diagram for showing the construction of a NCsystem for use in a WEDM apparatus which performs a method embodying thepresent invention;

FIG. 5 is a flowchart of an operation of checking graphic forms by amethod embodying the present invention;

FIG. 6 is a flowchart of details of a step S4 of the graphic checkingoperation by the method of FIG. 5;

FIG. 7 is a flowchart of details of a step S6 of the graphic checkingoperation by the method of FIG. 5; and

FIG. 8 is a diagram for showing an example of wire paths and a closedloop displayed on the screen of a CRT by the method embodying thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings.

Referring first to FIG. 4, there is shown an NC system for use in a WEDMapparatus which performs a method embodying the present invention.

In FIG. 4, like reference numerals indicate like portions, of the systemof FIG. 1, the descriptions of which are omitted herein. Further, inFIG. 4 reference numeral 2a indicates a memory which has functions ofthe memory 2 of the conventional system as well as functions of storinga machining locus of a wire electrode which is modified according towire radius modification processing (as described above), a flagindicating an occurrence of a closed loop and the positions of theclosed loop.

An operation of this system will be described hereinbelow with referenceto FIG. 5 which is a flowchart of an operation of checking graphic formsdisplayed on the screen of the CRT of the system of FIG. 4.

When the system is operated in a graphic form checking mode, the CPU 1reads an NC program for the graphic form checking operation (hereunderreferred to simply as the checking program) and data through an NCprogram I/O unit 200 from the paper tape I/O unit 3 or the I/O unit 6connected to the flexible disk 7 in step S1.

Then, the checking program advances to step S2 which causes an NCprogram analyzing unit 201 to analyze the NC program. As a result, if itis not necessary to perform wire radius modification processing, thechecking program skips to step S6 where the CRT 4 is controlled todisplay a machining path on the basis of the results of the analysis. Incontrast, if it is necessary to perform the wire radius modificationprocessing, the following processing is performed. That is, if theresults of the analysis effected in the step S2 indicate that the wireradius modification processing is needed, the checking program advancesto step S3 where the CPU 1 performs wire radius modification processing.Thereafter, the checking program advances to step S4 which causes aclosed loop discriminating unit 202 to perform closed loop checkingprocessing as follows.

As shown in FIG. 6, which is a flowchart showing details of the step S4,the CPU 1 first operates to obtain a segment C'D' of the machining locuswhich is obtained by subjecting a segment CD of the machining path tothe wire radius modification processing. Then, the checking programenters step S4-1 where the CPU 1 examines whether or not there is anyintersection of the thus obtained machining segment C'D' and themachining segments A'B' and B'C' the data of which has been stored inthe memory 2a. In this case, if there is no intersection, the checkingprogram then is allowed to advance to a step S6 which causes the CRT 4to display the actual machining locus. On the other hand, the CPU 1operates to detect whether or not the machining locus passes through thesame point twice or not. If the CPU 1 detects that there is anintersection E' as shown in FIG. 3 for instance by because the machininglocus A'-B'-C'-D' can be represented by A'-E'-B'-C'-E'-D' including thesame point E' twice, the CPU 1 determines that the segment C'D' formsthe closed loop E'-B'-C' with the segments A'B' and B'C'. This iscarried out in the step S4-2. Then, the checking program advances tostep S4-3 where the CPU 1 operates to register the data as to the closedloop E'-B'-C'-E' in the memory 2a as a portion 102 at which a closedloop occurs. Subsequently, the checking program advances to step S5where a flag indicating an occurrence of the closed loop is added.

Subsequent to the step S5, the checking program enters step S6 of whichdetails will be described hereinbelow with reference to a flowchart ofFIG. 7. That is, the checking program first enters S6-1 in which the CPU1 causes a CRT displaying unit 203 to display the machining path or themodified machining locus thereon. Thereafter, the checking programadvances to step S6-2 which examines whether the closed loop occurrenceflag is on or not. If not, the checking program is allowed to skip tobranching step S7. In contrast, in case of the flag being on, thefollowing processing will be effected. That is, the checking programfirst enters branching step S6-3, in which the CPU 1 fetches dataconcerning the closed loop from the memory 2a. Then, the checkingprogram advances to step S6-4 in which the CRT displaying unit 203controls the CRT display 4 to display the portion of the closed loop 102with a color different from colors indicating the remaining portions ofthe machining path. Then, the checking program advances to step S6-5 inwhich the closed loop occurrence flag is turned off. Thereafter, thechecking program advances to step S7 in which it is detected whether ornot the graphic form checking operation is to be terminated.

In summary, in case of checking graphic forms of FIG. 5, after thegraphic data of the segment C'D' are outputted to the CRT 4 to displaythe segment C'D' thereon, the CPU 1 confirms whether the closed loopoccurrence flag is turned on or not. If the flag is turned on, the CPU 1fetches the data concerning the portion where the closed loop 102(E'-B'-C'-E') occurs, from the memory 2a. Then, the closed loop 102(E'-B'-C'-E') is displayed on the display 4 with a loud color.

Further, upon completion of processing of a series of the NC program,the CPU 1 determines whether or not there is a termination code in stepS7. If not, the checking program returns to step S1 to continue theabove described series of operations. In contrast, if there is atermination code, the operation is terminated.

Although an NC system for use in a WEDM apparatus is describedhereinbefore as a preferred embodiment of the present invention,modifications are possible without departing from the essential scope ofthe present invention. More particularly, the present invention can beavailable in an NC system for use in a machining apparatus other thanthe wire cut EDM apparatus.

What is claimed is:
 1. A method for displaying a machining path of a machining tool on a display, said method comprising the steps of:(a) receiving NC data for a machining path; (b) modifying the NC data in accordance with a modification processing to produce modified NC data for a modified machining path; (c) detecting a closed loop within the modified machining path; (d) displaying at least a portion of the modified machining path on the display; and (e) distinguishably displaying the closed loop on the display when detected in step (c); wherein said detecting in step (c) comprises the steps of:storing data corresponding to the closed loop in a first memory; and setting a flag indicating the presence of a closed loop in a second memory.
 2. A method for displaying a machining path of a machining tool on a display, said method comprising the steps of:(a) receiving NC data for a machining path; (b) modifying the NC data in accordance with a modification processing to produce modified NC data for a modified machining path; (c) detecting a closed loop within the modified machining path; (d) displaying at least a portion of the modified machining path on the display; and (e) distinguishably displaying the closed loop on the display when detected in step (c); wherein said detecting in step (c) comprises the steps of:storing data corresponding to the closed loop in a first memory; and setting a flag indicating the presence of a closed loop in a second memory; and wherein said displaying in step (e) is performed in accordance with the flag set in the second memory.
 3. A system for displaying a machining path of a machining tool on a display, the system comprising:input means for receiving NC data for a machining path; display means for displaying information concerning the machining path; analyzing means for analyzing whether modification processing is necessary; modification means for modifying the NC data in accordance with the modification processing to produce modified NC data for a modified machining path; detection means for detecting a closed loop within the modified machining path; storage means for storing data corresponding to the modified machining path and the closed loop; and display control means for controlling the display of at least a portion of the modified machining path including the closed loop on said display means for distinguishably displaying the closed loop on said display means.
 4. A system according to claim 3, wherein said display control means controls said display means in accordance with the data corresponding to the modified machining path and the closed loop stored in said storage means.
 5. A system according to claim 3, wherein said system includes a wire cut electric discharge machining apparatus, and wherein the modification processing includes wire radius modification processing.
 6. A method of displaying numerical control (NC) program data for use in controlling a wire electrode of a wire electric discharge machining apparatus during a machining of a workpiece, the method comprises the steps of:(a) inputting an NC program representing a machining locus which is to be used to machine the workpiece; (b) analyzing the input NC program and determining whether or not the input NC program requires modification to compensate for the wire electrode of the wire electric discharge machining apparatus; (c) in response to a determination that modification is required, modifying the input NC program so that the NC program can be used to drive and control the wire electrode of the wire electrode discharge machining apparatus; (d) checking the NC program to determine if any closed loop is formed; (e) in response to a determination that a closed loop is formed, storing the segments of the NC program that forms the closed loop as a closed loop segment; and (f) displaying in a first color the NC program without the closed loop segment and displaying the closed loop segment in a second color, different from the first, thereby distinguishing the closed loop portion of the machining locus from the remaining portions of the locus. 